Turbocharged engines of the type used primarily in off highway trucks often have a pneumatically actuated wastegate valve for controlling the turbocharger speed and thus the boost pressure delivered to the intake manifold of the engine. The wastegate valve is normally disposed in the exhaust system of the engine and controls the speed of the turbocharger by modifying the volume of exhaust gasses directed to the turbine section of the turbocharger.
U.S. Pat. No. 4,697,421 dated Oct. 6, 1987 to Yutaka Otobe et. al. discloses a wastegate valve for bypassing engine exhaust flow from the turbine section and thereby control boost pressure. The wastegate valve is moved by a pneumatic actuator controlled by a control valve which varies the wastegate valve opening pressure based on boost pressure and intake manifold temperature. Maintaining the boost pressure at a target pressure may improve engine operating conditions and reduce engine knock at a given altitude. However, since there is no compensation for operating at different altitudes, the loss of boost at high altitudes and over boost at lower altitudes and ambient temperatures may occur. Therefore optimum operation of the engine is not achieved.
Wastegate valves have been successful in protecting the engine from excessive boost (peak cylinder pressure) at low altitudes (ambient temperatures) but have not been successfully used in situations where precision modulation of the wastegate valve is required. State of the art fluid operated wastegate control systems lack the responsiveness and accuracy required for good modulation. Therefore, in order to provide a higher degree of optimization of wastegate valve operation a more responsive and accurate control system must be provided.
In order to optimize wastegate control, maintain lower exhaust temperatures, and provide the right amount of boost at various air densities (different altitudes and different ambient air temperatures), it is necessary to provide a control system which considers various related control parameters. At present such a control system has not been provided.